Process for electrolytic pickling using nitric acid-free solutions

a technology of electrolysis and nitric acid, which is applied in the direction of crystal growth process, separation process, manufacturing tools, etc., can solve the problems of nitric acid replacement in electrolysis process applications typical of processes a) and c) and has not yet been solved, and nitric acid alone does not enable the same standards of surface roughness, opacity and surface quality

Inactive Publication Date: 2003-05-20
ACCIAI SPECIALI TERNI SPA +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

According to the technologies described previously, in the presence of electrolytic treatments with nitric acid solutions--technology a) or technology c)--an optimal finish of the product is obtained, but there emerge the well-known environmental problems linked to the emission toxic fumes of No.sub.x and to the presence of high concentrations of nitrate ions in the waste liquors.
The replacement of nitric acid in electrolytic process applications typical of processes a) and c) has, instead, not yet been solved.
The replacement of nitric acid with sulphuric acid alone does not enable the same standards of surface quality (lustre, passivatability) to be achieved.
However, in these conditions the attack proves inhomogeneous and leads to roughness and opacity of the surface.
As a result, a treatment using sulphuric acid alone determines excessive overall values of loss in weight, and consequently a final surface that is rough and has an opaque appearance.

Method used

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  • Process for electrolytic pickling using nitric acid-free solutions
  • Process for electrolytic pickling using nitric acid-free solutions
  • Process for electrolytic pickling using nitric acid-free solutions

Examples

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Embodiment Construction

To provide an example, an electrolytic pickling process according to the present invention will now be described for the treatment of a continuous strip of cold-rolled stainless steel sheet of the ferritic type (series 400) having a width of 1200 mm, previously treated with molten salts according to step A.1.

The electrolytic apparatus adopted is represented schematically in FIG. 1 as regards the essential structural elements and comprises a rectangular tank in which the useful path length of the strip in contact with the solution is 17.5 m.

FIG. 1 illustrates only the first basic electrolytic unit (module) supplied with electric current having an intensity of 3700 A. This is followed by a second, similar unit supplied with a 2100-A current.

In the diagram of FIG. 1, the first electrolytic region E.1 is represented, where the cathodic counter-electrode consists of a rectangular plate set beneath the strip, having the side parallel to the path of the strip 1200 mm long and the transvers...

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Abstract

A process for electrolytic pickling of stainless steel of the ferritic, martensitic, austenitic and duplex series as well as superaustenitic and superferritic steels, nickel or Ni/Cr-based super alloys, and titanium and its alloys is provided. The process utilizes an electrolytic pickling solution containing H2SO4 in a concentration of from 20 to 140 g/l and Fe3+ ions in a concentration of from 15 to 80 g/l, the Fe2+ ions being present a quantity corresponding to a Fe3+/Fe2+ ratio of >1 and preferably >3.

Description

This application is a United States national phase application filed under 35 U.S.C. .sctn.371 claiming priority from International Application PCT / EP99 / 06451, filed Sep. 2, 1999, and published under PCT Article 21(2) in English.The present invention regards a process for pickling and surface finishing of cold-rolled products or plane or long draw pieces made of stainless steel of the austenitic, ferritic and martensitic types, duplex steels, superaustenitic and superferritic steels, special alloys of nickel or nickel-chromium.The process, which has been devised in particular for continuous production, comprises a number of operating steps, at least one of which consists of a stage of electrolytic treatment, on processing lines in which the material to be pickled may or may not undergo a pre-treatment in a molten salt bath.Specifically, the present invention replaces the electrolytic bath in nitric acid and is followed by a treatment of passivation and / or final pickling, according t...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): C25F1/00C25F1/06C23C22/50C23C22/34C25F7/00
CPCC25F1/06
Inventor FORTUNATI, SANDRODEMERTZIS, YOANNISTRASATTI, STEFANOGIORDANI, PAOLOMUSSO, AUGUSTOMANCIA, FRANCO
Owner ACCIAI SPECIALI TERNI SPA
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